Gary T. Schwartz’s research while affiliated with Arizona State University and other places

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Publications (60)


Figure 1. Conceptual figure showing pathways by which oral health could influence cardiovascular disease and brain aging. Created with BioRender.com.
Figure 2. Cross-sectional age-related differences (locally weighted regression) in the number of healthy teeth (green), teeth with caries (black), teeth with exposed pulp (blue), and missing teeth (red).
Figure 3. Associations between cytokine levels and teeth with exposed pulp. Each line indicates the association between a different cytokine and the number of teeth with exposed pulp, caries, or missing, controlling for age, sex, and smoking (pack-years).
Figure 4. Associations between cardiovascular calcium and teeth with exposed pulp (red) by age, predicted from zero-inflated negative binomial models (Table 2).
Zero-inflated Negative Binomial Regression Models Examining Cardiovascular Calcium by the Number of Teeth with Exposed Pulp, Caries, and Absent Teeth. The Upper Section Displays Significant Predictors of Non-zero scores, While the Lower Section Displays the Significant Predictors of Inflated Scores of Zero

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Poor Oral Health Is Associated With Inflammation, Aortic Valve Calcification, and Brain Volume Among Forager-Farmers
  • Article
  • Full-text available

January 2024

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156 Reads

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3 Citations

The Journals of Gerontology Series A Biological Sciences and Medical Sciences

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Andrew T Ozga

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Poor oral health is associated with cardiovascular disease and dementia. Potential pathways include sepsis from oral bacteria, systemic inflammation, and nutritional deficiencies. However, in post-industrialized populations, links between oral health and chronic disease may be confounded because the lower socioeconomic exposome (poor diet, pollution, low physical activity) often entails insufficient dental care. We assessed tooth loss, caries, and damaged teeth, in relation to cardiovascular and brain aging among the Tsimane, a subsistence population living a relatively traditional forager-horticulturalist lifestyle with poor dental health, but minimal cardiovascular disease and dementia. Dental health was assessed by a physician in 739 participants aged 40-92 years with cardiac and brain health measured by chest computed tomography (CT) (n=728) and brain CT (n=605). A subset of 356 individuals aged 60+ were also assessed for dementia and mild cognitive impairment (n=33 impaired). Tooth loss was highly prevalent, with 2.2 teeth lost per decade and a 2-fold greater loss in women. The number of teeth with exposed pulp was associated with higher inflammation, as measured by cytokine levels and white blood cell counts, and lower body mass index. Coronary artery calcium and thoracic aortic calcium were not associated with tooth loss or damaged teeth. However, aortic valve calcification and brain tissue loss were higher in those that had more teeth with exposed pulp. Overall, these results suggest that dental health is associated with indicators of chronic diseases in the absence of typical confounds, even in a population with low cardiovascular and dementia risk factors.

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Aspects of molar form and dietary proclivities of African colobines

May 2023

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51 Reads

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1 Citation

Journal of Human Evolution

This study investigates aspects of molar form in three African colobine species: Colobus polykomos, Colobus angolensis, and Piliocolobus badius. Our samples of C. polykomos and P. badius are from the Taï Forest, Ivory Coast; our sample of C. angolensis is from Diani, Kenya. To the extent that protective layers surrounding seeds are hard, we predicted that molar features related to hard-object feeding would be more pronounced in Colobus than they are Piliocolobus, as seed-eating generally occurs at higher frequencies in species of the former. We further predicted that among the colobines we studied, these features would be most pronounced in Taï Forest C. polykomos, which feeds on Pentaclethra macrophylla seeds encased within hard and tough seed pods. We compared overall enamel thickness, enamel thickness distribution, absolute crown strength, cusp tip geometry, and flare among molar samples. Sample sizes per species and molar type varied per comparison. We predicted differences in all variables except overall enamel thickness, which we expected would be invariant among colobines as a result of selection for thin enamel in these folivorous species. Of the variables we examined, only molar flare differed significantly between Colobus and Piliocolobus. Our findings suggest that molar flare, an ancient feature of cercopithecoid molars, was retained in Colobus but not in Piliocolobus, perhaps as a result of differences in the seed-eating proclivities of the two genera. Contrary to predictions, none of the aspects of molar form we investigated tracked current dietary differences in seed-eating between the two Colobus species. Finally, we explored the possibility that molar flare and absolute crown strength, when analyzed together, might afford greater differentiation among these colobine species. A multivariate t test of molar flare and absolute crown strength differentiated C. polykomos and P. badius, possibly reflecting known niche divergence between these two sympatric Taï Forest species.


Comparative description and taxonomic affinity of 3.7-million-year-old hominin mandibles from Woranso-Mille (Ethiopia)

December 2022

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74 Reads

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3 Citations

Journal of Human Evolution

Fossil discoveries of early Australopithecus species from Woranso-Mille have played a significant role in improving our understanding of mid-Pliocene hominin evolution and diversity. Here, we describe two mandibles with dentitions, recovered from sediments immediately above a tuff radiometrically dated to 3.76 ± 0.02 Ma, and assess their taxonomic affinity. The two mandibles (MSD-VP-5/16 and MSD-VP-5/50) show morphological similarities with both Australopithecus anamensis and Australopithecus afarensis. Some of the unique features that distinguish Au. anamensis from Au. afarensis are present in the mandibles, which also share a few derived features with Au. afarensis. Their retention of more Kanapoi Au. anamensis-like traits, compared to the fewer derived features they share with Au. afarensis, and the presence of Au. anamensis at Woranso-Mille in 3.8-million-year-old deposits, lends support to their assignment to Au. anamensis. However, it is equally arguable that the few derived dentognathic features they share with Au. afarensis could be taxonomically more significant, making it difficult to conclusively assign these specimens to either species. Regardless of which species they are assigned to, the mosaic nature of the dentognathic morphology and geological age of the two mandibles lends further support to the hypothesized ancestor–descendant relationship between Au. anamensis and Au. afarensis. However, there is now limited fossil evidence indicating that these two species may have overlapped in time. Hence, the last appearance of Au. anamensis and first appearance of Au. afarensis are currently unknown. Recovery of Australopithecus fossils from 4.1 to 3.8 Ma is critical to further address the timing of these events.


Molar form, enamel growth, and durophagy in Cercocebus and Lophocebus

July 2022

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68 Reads

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6 Citations

American Journal of Biological Anthropology

Objectives To test the hypothesis that differences in crown structure, enamel growth, and crown geometry in Cercocebus and Lophocebus molars covary with differences in the feeding strategies (habitual vs. fallback durophagy, respectively) of these two genera. Relative to Lophocebus molars, Cercocebus molars are predicted to possess features associated with greater fracture resistance and to differ in enamel growth parameters related to these features. Materials and Methods Sample proveniences are as follows: Cercocebus atys molars are from the Taï Forest, Ivory Coast; Lophocebus albigena molars are from a site north of Makoua, Republic of Congo; and a Lophocebus atterimus molar is from the Lomako Forest, Democratic Republic of Congo. For μCT scans on which aspects of molar form were measured, sample sizes ranged from 5 to 35 for Cercocebus and 3 to 12 for Lophocebus . A subsample of upper molars was physically sectioned to measure enamel growth variables. Results Partly as a function of their larger size, Cercocebus molars had significantly greater absolute crown strength (ACS) than Lophocebus molars, supporting the hypothesis. Greater crown heights in Cercocebus are achieved through faster enamel extension rates. Also supporting the hypothesis, molar flare and proportional occlusal basin enamel thickness were significantly greater in Cercocebus . Relative enamel thickness (RET), however, was significantly greater in Lophocebus . Discussion If ACS is a better predictor of fracture resistance than RET, then Cercocebus molars may be more fracture resistant than those of Lophocebus . Greater molar flare and proportional occlusal basin thickness might also afford Cercocebus molars greater fracture resistance.


Fig. 1. Macaque skull indicating study landmarks and masticatory muscle mechanics. (A) Lateral view of skull (left), basal view of cranium (center), and occlusal view of mandible (right) illustrating the 38 landmarks (see table S8) used to capture the position of the three principal masticatory adductor muscles and overall masticatory configuration. (B) Lateral view of the position and orientation of muscle lines of action (MLAs) for the masseter (left), temporalis (center), and medial pterygoid (right) muscles, as well as the point (blue colored circle) where each MLA intersects the TOS plane (dashed line). Checkered circles indicate landmarks that are out of view. See text and the Supplementary Materials for details. Photo credit: H. Glowacka, University of Arizona.
Fig. 2. Macaque skull indicating overall masticatory configuration and biomechanical variables. (A) Intersection points of each MLA from Fig. 1 were projected onto the occlusal plane, and their average position was used to represent the point at which the AMRV (red arrow) crosses the TOS plane, projected onto the occlusal plane (red square). (B) Occlusal view of mandible illustrating (left half of image): the position of the AMRV at the level of the occlusal plane (red square), extended laterally by the red dashed line, and the main masticatory regions where the CLM predicts bite points could be (regions I and II) and should not be (region III) located; (right half of image) the measurement resultant molar taken from the position of the AMRV to the distalmost border of each successively emerging mandibular molar (dp 4 , M 1-3 ) and MAL (gray dashed arrow), comprising the summed linear distance from the AMRV, through the last emerged molar and each interproximal space along the entire mandibular arch, terminating anteriorly at infraoral (point no. 29, the midline point at apex of the septum between the mandibular central incisors; see Fig. 1A and table S8). (C) Occlusal view of juvenile mandible mapping out the regions of the CLM and the location of the measurements, resultant molar, and MAL [colored regions and arrows indicate the same as in (B)]. Checkered circles in (B) and (C) indicate landmarks that are out of view. See text and the Supplementary Materials for details. Photo credit: H. Glowacka, University of Arizona.
Fig. 4. Growth of MAL. MAL growth for ontogenetic series of known-age individuals representing a subset of five primate species. Breakpoints (indicated by vertical dashed lines) indicate ages at growth cessation and are determined by segmented regression (see text for details).
Fig. 5. Relationship between life history and MAL growth rate/cessation. PGLS results for the relationships between PC1 and MAL growth rate (left) and MAL growth cessation (right). PC1 scores derived from a PCA of five primate species and includes brain size and the following life history variables: age at first reproduction, IBI, and gestation length.
Primate molar emergence and MAL growth cessation ages.
A biomechanical perspective on molar emergence and primate life history

October 2021

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142 Reads

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7 Citations

Science Advances

The strong relationship between M1 emergence age and life history across primates provides a means of reconstructing fossil life history. The underlying process that leads to varying molar emergence schedules, however, remains elusive. Using three-dimensional data to quantify masticatory form in ontogenetic samples representing 21 primate species, we test the hypothesis that the location and timing of molar emergence are constrained to avoid potentially dangerous distractive forces at the temporomandibular joint (TMJ) throughout growth. We show that (i) molars emerge in a predictable position to safeguard the TMJ, (ii) the rate and duration of jaw growth determine the timing of molar emergence, and (iii) the rate and cessation age of jaw growth is related to life history. Thus, orofacial development is constrained by biomechanics throughout ontogeny. This integrative perspective on primate skull growth is consistent with a long sought-after causal explanation underlying the correlation between molar emergence and life history.


Drimolen cranium DNH 155 documents microevolution in an early hominin species

January 2021

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1,561 Reads

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37 Citations

Nature Ecology & Evolution

Paranthropus robustus is a small-brained extinct hominin from South Africa characterized by derived, robust craniodental morphology. The most complete known skull of this species is DNH 7 from Drimolen Main Quarry, which differs from P. robustus specimens recovered elsewhere in ways attributed to sexual dimorphism. Here, we describe a new fossil specimen from Drimolen Main Quarry, dated from approximately 2.04–1.95 million years ago, that challenges this view. DNH 155 is a well-preserved adult male cranium that shares with DNH 7 a suite of primitive and derived features unlike those seen in adult P. robustus specimens from other chronologically younger deposits. This refutes existing hypotheses linking sexual dimorphism, ontogeny and social behaviour within this taxon, and clarifies hypotheses concerning hominin phylogeny. We document small-scale morphological changes in P. robustus associated with ecological change within a short time frame and restricted geography. This represents the most highly resolved evidence yet of microevolutionary change within an early hominin species.


A comprehensive survey of Retzius periodicities in fossil hominins and great apes

October 2020

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95 Reads

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9 Citations

Journal of Human Evolution

Recent studies have provided great insight into hominin life history evolution by utilizing incremental lines found in dental tissues to reconstruct and compare the growth records of extant and extinct humans versus other ape taxa. Among the hominins, studies that have examined Retzius periodicity (RP) variation have come to contradictory conclusions in some instances. To clarify RP variation among hominins and better place this variation in its broader evolutionary context, we conduct the most comprehensive analysis of published RP values for hominins and great apes to date. We gathered all available data from the literature on RP data from extant humans, great apes, and fossil hominins and assessed their variation using parametric and nonparametric analyses of variance. We also performed phylogenetic generalized least-squares regressions of RP data for these taxa as well as a larger set of hominoids for which RP data have been published against data for body mass, encephalization, and mean semicircular canal radius (a proxy for metabolic rate). Our results show that modern humans have a mean RP significantly differing from that of other hominins. Pongo also is significantly different from nearly all other taxa in all analyses. Our results also demonstrate that RP variation among hominins scales with respect to body mass, encephalization, and semicircular canal radius similarly to other hominids but that modern humans and Pongo stand out in this regard. Operating within the hypothesis that RP reflects autonomic biorhythms that regulate multiple life history variables, our results reinforce the idea that Homo sapiens has evolved a life history distinct from other hominins, even from other members of Homo, and suggest that many of these life history differences may be driven by hypothalamic output from the brain.


Enamel thickness variation in the deciduous dentition of extant large‐bodied hominoids

August 2020

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67 Reads

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5 Citations

American Journal of Physical Anthropology

Objectives Enamel thickness features prominently in hominoid evolutionary studies. To date, however, studies of enamel thickness in humans, great apes, and their fossil relatives have focused on the permanent molar row. Comparatively little research effort has been devoted to tissue proportions within deciduous teeth. Here we attempt to fill this gap by documenting enamel thickness variation in the deciduous dentition of extant large‐bodied hominoids. Materials and methods We used microcomputed tomography to image dental tissues in 80 maxillary and 78 mandibular deciduous premolars of Homo sapiens , Pan troglodytes , Gorilla , and Pongo . Two‐dimensional virtual sections were created from the image volumes to quantify average (AET) and relative (RET) enamel thickness, as well as its distribution across the crown. Results Our results reveal no significant differences in enamel thickness among the great apes. Unlike the pattern present in permanent molars, Pongo does not stand out as having relatively thicker‐enameled deciduous premolars than P. troglodytes and Gorilla. Humans, on the other hand, possess significantly thicker deciduous premolar enamel in comparison to great apes. Following expectations from masticatory biomechanics, we also find that the “functional” side (protocone, protoconid) of deciduous premolars generally possesses thicker enamel than the “nonfunctional” side. Discussion Our study lends empirical support to anecdotal observations that patterns of AET and RET observed for permanent molars of large‐bodied apes do not apply to deciduous premolars. By documenting enamel thickness variation in hominoid deciduous teeth, this study provides the comparative context to interpret rates and patterns of wear of deciduous teeth and their utility in life history reconstructions.


Age at first molar emergence in Pan troglodytes verus and variation in the timing of molar emergence among free-living chimpanzees

August 2020

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26 Reads

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8 Citations

Journal of Human Evolution

Age at lower first molar (M1) emergence is a commonly used proxy for inferring life-history scheduling in fossil primates, but its utility is dependent on knowing to what extent extant populations vary in this datum and how this variation correlates with the scheduling of life-history variables. Here, we address the first of these issues among extant chimpanzees. While age at M1 emergence has been documented in several live individuals from the Kanyawara population of Pan troglodytes schweinfurthii in Uganda, it has been estimated for only one individual of Pan troglodytes verus, based on a deceased animal from the Taï Forest in Côte d’Ivoire. To further explore interpopulation variation in this variable in chimpanzees, and using dental histology, we calculated ages at death for two wild-shot individuals of P. t. verus with erupting M1, both collected in Liberia during the mid-1950s, and estimated ages at M1 emergence from the ages at death. The overall range for these two individuals is ∼4.2–4.6 yr, compared with an age of ∼3.7 yr for the individual from the Taï Forest, and <2.5–3.3 yr for the several individuals of P. t. schweinfurthii. While the absolute range of ∼2 yr in these samples combined is little greater than in captive chimpanzees, the disparity between the samples of P. t. schweinfurthii and P. t. verus is striking, although it cannot be determined if this disparity represents a subspecies difference or simply population differences expressed in two different subspecies. While life-history data are unavailable for the population to which the Liberian chimpanzees belonged, the difference in M1 emergence ages between these individuals and those from Kanyawara still suggests caution when attempting even broad life-history inference in fossil apes and hominins based on age at M1 emergence.


Fracture mechanics, enamel thickness and the evolution of molar form in hominins

January 2020

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100 Reads

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24 Citations

As the tissue most directly responsible for breaking down food in the oral cavity, the form and function of enamel is obviously of evolutionary significance in humans, non-human primates and other vertebrates. Accordingly, a standard metric, relative enamel thickness (RET), has been used for many decades to provide insights into vertebrate and human palaeobiology. Relatively thick enamel has evolved many times in vertebrates including hominoids (the group to which living humans and fossil hominins belong), and this pattern is thought to provide information about taxonomy, phylogeny, functional anatomy and diet. In particular, relatively thick enamel is thought to make tooth crowns strong so that they resist fractures associated with eating mechanically resistant foods. Here, we use current models of tooth biomechanics to show that RET is at best only moderately informative of function and diet in living hominoids and fossil hominins, and at worst provides misleading information. We propose a new metric, absolute crown strength, to assess the resistance of teeth to fracture, and identify what may be a novel characteristic of tooth strength in fossil hominins.


Citations (53)


... Various possible mechanisms linking the association of periodontal disease with dementia have been investigated [24,25]. Bacterial endotoxins as lipopolysaccharides (LPS) and pro-inflammatory products such as C-reactive protein (CRP), tumor necrosis factoralpha (TNF-alpha), and interleukin-1 and -6 (IL-1, -6) resulting from periodontal disease have been suggested to increase the risk of nervous system inflammation entering via the oral cavity [17]. ...

Reference:

Tooth Loss in Periodontitis Patients—A Risk Factor for Mild Cognitive Impairment: A Systematic Review and Meta—Analysis
Poor Oral Health Is Associated With Inflammation, Aortic Valve Calcification, and Brain Volume Among Forager-Farmers

The Journals of Gerontology Series A Biological Sciences and Medical Sciences

... This contrasts with results from studies based on absolute dental size [24]. These findings imply that, despite the significant diversity in dietary habits among African and Asian Colobinae related to different environmental adaptations [113][114][115], they display very similar molar patterns relative to body size, supporting their classification as folivorous primates [103,[116][117][118]. ...

Aspects of molar form and dietary proclivities of African colobines
  • Citing Article
  • May 2023

Journal of Human Evolution

... Na výbrusech zubů jsou patrné v podobě zesílených, akcentovaných linií (stresových linií), a to jak ve sklovině, tak i v dentinu (Dean 2000;Smith 2008;Smith -Tafforeau 2008;FitzGerald -Rose 2008;Hillson 2014). Jelikož se tyto události a vývojová narušení objevují ve vývoji v určitém čase, jsou zaznamenány v mikrostruktuře všech zubů, které se v čase působení stresové události vyvíjely (Dirks et al. 2002;Schwartz -Dean 2008; Obr. 1. Histologický výbrus rostoucího lidského zubu (třetí horní stolička pravé strany) zobrazený v procházejícím světle pomocí světelného mikroskopu (část vlevo) a schematické znázornění vnitřní mikrostruktury a inkrementálních linií (část vpravo): E -sklovina, D -dentin, edj -dentino-sklovinná hranice, dh -dentinový hrot, ep -sklovinná prizmata, dt -dentinové tubuly, ae -apoziční/hrbolková sklovina, ie -imbrikační/laterální sklovina, Rl -Retziusovy linie, Al -Andresenovy linie, cs -příčné linie, vE -von Ebnerovy linie, al -akcentované/ stresové linie. ...

Charting the chronology of developing dentitions
  • Citing Chapter
  • February 2008

... Consequently, because P. pygmaeus spends more time feeding on hard-object fallback foods, they should display thicker enamel than Sumatran orangutans. However, recent studies suggested that relative enamel thickness is not an accurate measure of how teeth withstand occlusal loads (Guatelli-Steinberg et al., 2023;Guatelli-Steinberg et al., 2024;Guatelli-Steinberg, Schwartz, et al., 2022;Schwartz et al., 2020). It is also possible that the differences in feeding behavior observed in Sumatran and Bornean orangutans emerged only recently (Smith et al., 2012). ...

Molar form, enamel growth, and durophagy in Cercocebus and Lophocebus

American Journal of Biological Anthropology

... What are the implications for the evolution of hominin life history? Because teeth are central to masticatory function, evolutionary changes in their maturation schedules tend to reflect changes in masticatory biomechanics 43 and in the timing of dietary transitions during an individual's life, from breastfeeding to solid foods and from nutritional dependence to independence. These changes, in turn, are thought to reflect evolutionary changes in the allocation of metabolic resources to cerebral, somatic and reproductive maturation, and thus changes in life history. ...

A biomechanical perspective on molar emergence and primate life history

Science Advances

... Considering that the mandible and teeth are substantially smaller and that some nonmetric features differ from P. boisei (and P. aethiopicus) and P. robustus (Wood, 1991;Curnoe, 2006;Grine, 2005; Table 4), which also explains why the specimen was lumped into Homo for decades, it appears evident that SK 15 represents another species of Paranthropus that was previously unrecognized, P. capensis. The species very likely split from P. robustus before 2 Ma at a time when this taxon showed a variable degree of size and robustness (Martin et al., 2020). The presence of other P. capensis specimens mixed among the current hypodigm of P. robustus should be tested further, in particular by revising the fossil assemblages from Swartkrans, Drimolen, and Kromdraai that include most of the Paranthropus specimens from southern Africa. ...

Drimolen cranium DNH 155 documents microevolution in an early hominin species

Nature Ecology & Evolution

... Sequences of dental development indicate that the early Homo species, including erectus, had a pace of life history similar to that of contemporary and fossil African apes. The prolonged life-history schedule of modern humans appears in the later stages of human evolution and possibly, again, with the origin of Neanderthals and modern humans (82), an inference supported by many other aspects of the fossil record (83)(84)(85). The fast tempo of maturity of early Homo species suggests that mere larger brains and body sizes were not the primary selective agent for prolonged maturity and extended life stages (82)(83)(84). ...

A comprehensive survey of Retzius periodicities in fossil hominins and great apes
  • Citing Article
  • October 2020

Journal of Human Evolution

... However, roots cannot be analysed with a dental cast. Several studies have evaluated intact deciduous teeth derived from hominid fossils [Bermúdez de Castro et al., 2017;Pan et al., 2021;Ortiz et al., 2020]. These findings are needed to obtain odontometric data, which are useful in many fields, including anthropology, genetics, forensic science, and dentistry. ...

Enamel thickness variation in the deciduous dentition of extant large‐bodied hominoids
  • Citing Article
  • August 2020

American Journal of Physical Anthropology

... SD = 0.3) (Esan et al. 2018). Comparatively, free-living Pan troglodytes chimpanzees erupt the first lower molars no later than 4.6 years old (Kelley et al. 2020). Given the totality of the mosaic nature of Homo naledi dental development and the human-like enamel formation timing for the first molar, we hypothesise a human-like timing of maturity and estimate the early juvenile Homo naledi are at least about 5.0 − 6.6 years of age. ...

Age at first molar emergence in Pan troglodytes verus and variation in the timing of molar emergence among free-living chimpanzees
  • Citing Article
  • August 2020

Journal of Human Evolution

... Consequently, because P. pygmaeus spends more time feeding on hard-object fallback foods, they should display thicker enamel than Sumatran orangutans. However, recent studies suggested that relative enamel thickness is not an accurate measure of how teeth withstand occlusal loads (Guatelli-Steinberg et al., 2023;Guatelli-Steinberg et al., 2024;Guatelli-Steinberg, Schwartz, et al., 2022;Schwartz et al., 2020). It is also possible that the differences in feeding behavior observed in Sumatran and Bornean orangutans emerged only recently (Smith et al., 2012). ...

Fracture mechanics, enamel thickness and the evolution of molar form in hominins